JP3980035B2 - LIGHT EMITTING ELEMENT AND MANUFACTURING METHOD THEREOF - Google Patents

Description

  The present invention relates to a light emitting device having a sufficiently wide band gap to emit light from visible to near ultraviolet and a method for producing the same, and in particular, a colorless and transparent conductor that transmits light from the visible region to the ultraviolet region can be obtained. The present invention relates to a light-emitting element that can have a vertical structure using the conductor as a substrate and can also have a light extraction surface on the substrate side, and a manufacturing method thereof.

  As a conventional light emitting device, a device in which an n-type layer and a p-type layer made of GaN are stacked on a substrate made of SiC is known (see, for example, Patent Document 1).

  SiC has brownish-brown transparency and transmits visible light up to about 427 nm, so that it can transmit emitted light from the substrate side.

  In this light emitting device using SiC, a SiC thin film is epitaxially grown on a single crystal wafer of SiC to form a SiC epitaxial substrate, and an n-type layer and a p-type layer made of GaN are formed on the substrate, and these are formed. It is manufactured by cutting out into a plurality of light emitting elements.

As a conventional light-emitting element, there is one in which a GaN-based semiconductor light-emitting layer is formed on a sapphire substrate and the electrode arrangement is a horizontal structure (for example, see Patent Document 2).
Further, as a conventional EFG (Edge defined film Fed Growth) method, there is a method in which a rare earth vanadate single crystal is formed using an iridium die and a crucible (see, for example, Patent Documents 3 and 4).
Further, as a conventional EFG method, there is a method for producing a rutile plate-like single crystal (see, for example, Patent Document 5).
Further, as a conventional method for growing a β-Ga ₂ O ₃ single crystal, there is a method using an FZ method or a flux method (for example, see Non-Patent Document 1).
Further, as a conventional PLD method, there is a method in which a (0001) -oriented single crystal thin film having a hexagonal crystal structure such as ZnO is grown on a (111) single crystal substrate of a cubic oxide (for example, Patent Documents). 6).
JP 2002-255692 A (paragraph 0008) Japanese Patent No. 2918139 (paragraph 0024, FIG. 2) Japanese Patent Laid-Open No. 10-231199 (paragraphs 0004 to 0008, FIG. 1) Japanese Patent Laid-Open No. 11-157987 (paragraph 0008, FIG. 1) Japanese Patent No. 2814325 (paragraph 0005, FIG. 1) JP 2002-68889 A (paragraph 0005) M. Saurat, A. Revcolevschi, “Rev. Int. Hautes Temper. Et Refract”, 1971,8. P. 291

  However, since SiC has poor crystallinity of a single crystal wafer and has so-called micropipe defects penetrating in the vertical direction of the single crystal, it must be cut out by forming an n-type layer and a p-type layer avoiding the micropipe defects. Therefore, there is a problem that productivity as a light emitting element is poor.

  Further, SiC transmits light up to the blue region, but does not transmit light in the ultraviolet region. Therefore, when the emitted light is extracted from the substrate side, the substrate side cannot be used as an ultraviolet light extraction surface because it cannot transmit the ultraviolet light of the GaN emitted light that emits light from the visible region to the ultraviolet region. There is a problem. In addition, since SiC is colored, there is a problem that a part of the emission wavelength is absorbed in the light transmitted through SiC.

  Accordingly, an object of the present invention is to obtain a colorless and transparent conductor that transmits light in the visible region to the ultraviolet region, and the conductor can be used as a substrate to form a vertical structure. Another object of the present invention is to provide a light emitting element that can be used as a light extraction surface and a method for manufacturing the light emitting element. Another object of the present invention is to provide a light-emitting element with high productivity and a method for manufacturing the same.

An embodiment of the present invention includes a Ga ₂ O ₃ single crystal substrate and a pn junction formed on the substrate, the substrate including an additive for adjusting a lattice constant or a band gap, and the pn The junction includes a GaN compound semiconductor thin film of one conductivity type formed on the substrate and a GaN of another conductivity type opposite to the one conductivity type formed on the GaN compound semiconductor thin film of one conductivity type. Provided is a light emitting device formed by a compound semiconductor thin film.

  In another embodiment of the present invention, one or more selected from the group consisting of Cu, Ag, Zn, Cd, Al, In, Si, Ge, and Sn can be used as the additive.

In another embodiment of the present invention, the substrate is made of (Al _x In _y Ga _(1-xy) ) ₂ O ₃ (where 0 ≦ x <1, 0 ≦ y <1, 0 ≦ x + y < 1).

  According to the present invention, it is possible to provide a GaN-based light-emitting device using a transparent conductor and a material capable of producing a bulk single crystal as a substrate, and a method for manufacturing the same, and electrodes are attached to the top and bottom of the light-emitting device. Improved the productivity and improved the light extraction efficiency.

  Further, by using an oxide containing Ga as a main component for the substrate, a colorless and transparent conductor that transmits light in the visible region to the ultraviolet region can be obtained, and the conductor is used as a substrate to form a vertical structure. Thus, it is possible to provide a light emitting element and a method for manufacturing the same, in which the substrate side can also be a light extraction surface.

In addition, it is possible to obtain a Ga ₂ O ₃ single crystal having better workability than sapphire and SiC, which are conventional substrate materials.

<Board>
Since β-Ga ₂ O ₃ has conductivity, an electrode having a vertical structure can be produced, and as a result, the entire device can be used as a current path, so that the current density can be lowered. The life of the light emitting element can be extended.

Actually, as a result of measuring the specific resistance of the β-Ga ₂ O ₃ substrate having n-type conductivity, a value of about 0.1 Ω · cm is obtained at room temperature as shown in FIG. In addition, since the temperature change of the specific resistance is small in the temperature range used as the light emitting element, stability as the light emitting element can be obtained.

  Further, since the electrode structure is a vertical type, it is not necessary to expose the n layer by etching, so that the number of element manufacturing steps can be reduced, and the number of elements per unit area of the substrate can be increased.

  When using sapphire as the substrate, the electrode structure is horizontal, so after the growth of the III-V group compound semiconductor thin film, the n layer is exposed and the n electrode is attached. Necessary. However, when the electrode structure is a vertical type, the masking and etching processes described above are not necessary as in the case of a GaAs light emitting device.

  In the case of SiC, there are many phases such as 3C, 4H, 6H, and 15R, and it is difficult to obtain a single-phase substrate. Since the hardness is very high and the workability is poor, it is difficult to obtain a flat substrate, and when viewed on an atomic scale, there are many steps with different phases on the substrate surface. When a thin film is grown on the substrate, many films having different crystallinity and defect density grow. As described above, in the case of SiC, innumerable nuclei with different qualities grow on one substrate, and as a result, the film grows in a form in which they are combined, so it is extremely difficult to improve the quality of the film. Actually, the lattice mismatch between SiC and GaN is theoretically said to be 3.4%, but the actual lattice mismatch is extremely large for the reasons described above.

On the other hand, since β-Ga ₂ O ₃ is a single phase and is flat on an atomic scale, there is no practical large lattice mismatch as seen in SiC. From the viewpoint of the band gap, in the case of SiC, for example, in the case of 6H-SiC, it is 3.03 eV, so it is opaque in a wavelength region of about 427 nm or less. Considering that the light emitting region of the III-V group compound semiconductor is about 550 to 380 nm, it must be said that the wavelength range available for SiC is about 2/3 of the wavelength range. On the other hand, in the case of β-Ga ₂ O ₃ , since it transmits up to about 260 nm, it can be used in the entire wavelength range of the light emitting region of the III-V group compound semiconductor, particularly in the ultraviolet region.

The substrate used in the invention is based on β-Ga ₂ O ₃ , but Ga added with one or more selected from the group consisting of Cu, Ag, Zn, Cd, Al, In, Si, Ge, and Sn is added. You may comprise with the oxide which made the main component. The effect of these additive elements is to control the lattice constant or band gap energy. For example, a gallium oxide represented by (Al _x In _y Ga _(1-xy) ) ₂ O ₃ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) is used. it can.

<Coefficient of thermal expansion>
In terms of thermal expansion, the coefficient of thermal expansion of GaN is 5.6 × 10 ⁻⁶ / K, whereas the value of β-Ga ₂ O ₃ is 4.6 × 10 ⁻⁶ / K, It is comparable to sapphire (4.5 × 10 ⁻⁶ / K) and has an advantage over 6H—SiC (3.5 × 10 ⁻⁶ / K). The difference in thermal expansion coefficient is also a major factor from the viewpoint of the quality of the grown film.

<Bulk single crystal>
The biggest feature of β-Ga ₂ O ₃ is that a bulk single crystal can be obtained. Bulk single crystals have always been obtained from the near infrared to red region centered on GaAs-based materials, and a film with extremely small lattice mismatch has been obtained on the conductive substrate. Accordingly, it is easy to manufacture a light-emitting element with low cost and high efficiency. A material expected to be a GaN-based or ZnSe-based so-called blue light-emitting element has been virtually impossible to produce a bulk single crystal. For this reason, development of a bulk single crystal that is conductive and transparent in the light emitting region and has a small lattice mismatch has been carried out. Even today, this problem is not essentially solved. On the other hand, the β-Ga ₂ O ₃ substrate provided by the present invention drastically solves these problems. Since a bulk single crystal having a diameter of 2 inches can be obtained by the EFG method or the FZ method, the development of light emitting elements in the blue to ultraviolet region can be handled in the same manner as the GaAs light emitting elements.

<Ga ₂ O ₃ single crystal by EFG method>
FIG. 2 shows a crucible used for the EFG method. This crucible 6 is inserted into an EFG method pulling furnace (not shown). The crucible 6 is made of, for example, iridium and includes a slit die 8 having a slit 8a that raises the β-Ga ₂ O ₃ melt 9 by capillary action.

In the EFG method, a single crystal is grown as follows. A predetermined amount of β-Ga ₂ O ₃ as a raw material is put in the crucible 6 and heated to be dissolved to obtain a β-Ga ₂ O ₃ melt 9. The _β-Ga 2 _{O 3} melt 9 by a slit 8a for forming the slit die 8 arranged in the crucible 6 is raised to the slit die 8 top by capillary action, the seed crystal 7 _β-Ga 2 _{O 3} melt 9 Are brought into contact with each other and cooled to form a grown crystal 10 having a cross section of an arbitrary shape.

Specifically, 75 g of gallium oxide raw material is placed in an iridium crucible 6 having an inner diameter of 48.5 mm, a wall thickness of 1.5 mm, and a height of 50 mm, and is 3 mm thick × 20 mm wide × 40 mm high, with a slit spacing of 0.5 mm. The slit die 8 was installed. The crucible 6 was maintained in a normal nitrogen atmosphere, 1 atm, 1760 ° C., and the oxygen partial pressure was maintained at 5 × 10 ⁻² atm, and the β-Ga ₂ O ₃ melt was raised by capillary action in the slit 8a. 9 was brought into contact with a seed crystal 7 of β-Ga ₂ O ₃ to grow a single crystal at a speed of 1 mm / h.

Since the single crystal defined by the shape of the slit die 8 is grown above the slit die 8, the temperature gradient at the crystal growth interface can be made extremely small as compared with the CZ method. Furthermore, since the β-Ga ₂ O ₃ melt 9 is supplied through the slit 8a and the crystal growth rate is faster than the diffusion rate in the β-Ga ₂ O ₃ melt 9, the β-Ga ₂ O ₃ melt 9 and the composition fluctuation of the β-Ga ₂ O ₃ melt 9 can be extremely reduced. Therefore, a high quality single crystal can be produced. In addition, since the shape of the grown crystal 10 can be defined by the shape of the slit die 8, it is possible to easily increase the size of the single crystal by increasing the size of the slit die 8. As described above, the EFG method makes it possible to increase the size and quality of a Ga ₂ O ₃ single crystal, which has been difficult with a method such as the CZ method.

<Ga ₂ O ₃ single crystal by FZ method>
FIG. 3 shows an infrared heating single crystal manufacturing apparatus for manufacturing a β-Ga ₂ O ₃ single crystal by the FZ method (floating zone method). This infrared heating single crystal manufacturing apparatus 100 includes a quartz tube 102, a seed rotating unit 103 that holds and rotates a β-Ga ₂ O ₃ seed crystal (hereinafter referred to as “seed crystal”) 107, and β-Ga ₂ O. ₃ A material rotating unit 104 that holds and rotates a polycrystalline material (hereinafter abbreviated as “polycrystalline material”) 109, a heating unit 105 that heats and melts the polycrystalline material 109, a seed rotating unit 103, and a material rotating unit. 104 and a control unit 106 that controls the heating unit 105.

  The seed rotating unit 103 includes a seed chuck 133 that holds the seed crystal 107, a lower rotating shaft 132 that transmits rotation to the seed chuck 133, a lower driving unit 131 that rotates the lower rotating shaft 132 in the normal direction and moves it in the vertical direction. Is provided.

  The material rotating unit 104 moves the material chuck 143 that holds the upper end 109a of the polycrystalline material 109, the upper rotating shaft 142 that transmits the rotation to the material chuck 143, the upper rotating shaft 142 forward and backward, and the vertical rotation. And an upper drive unit 141 to be operated.

  The heating unit 105 houses a halogen lamp 151 that heats and melts the polycrystalline material 109 from the radial direction, and an elliptical mirror that collects the light emitted from the halogen lamp at a predetermined portion of the polycrystalline material 109. 152 and a power supply unit 153 that supplies power to the halogen lamp 151.

The quartz tube 102 accommodates a lower rotating shaft 132, a seed chuck 133, an upper rotating shaft 142, a material chuck 143, a polycrystalline material 109, a β-Ga ₂ O ₃ single crystal 108 and a seed crystal 107. The quartz tube 102 can be sealed by being supplied with a mixed gas of oxygen gas and nitrogen gas as an inert gas.

In order to grow a β-Ga ₂ O ₃ single crystal, the following method is used. First, a seed crystal 107 and a polycrystalline material 109 are prepared. That is, the seed crystal 107 is, for example, a β-Ga ₂ O ₃ single crystal cut out along the cleavage plane, and has a diameter of 1/5 or less of a grown crystal or a cross-sectional area of 5 mm ² or less. -Ga ₂ O ₃ has a strength that does not break during the growth of a single crystal. The polycrystalline material 109 is obtained by filling a predetermined amount of Ga ₂ O ₃ powder in a rubber tube (not shown), cold compressing at 500 MPa, and then sintering at 1500 ° C. for 10 hours.

  Next, one end of the seed crystal 107 is held on the seed chuck 133, and the upper end portion 109 a of the rod-shaped polycrystalline material 109 is held on the material chuck 143. The upper and lower positions of the upper rotating shaft 142 are adjusted to bring the upper end of the seed crystal 107 into contact with the lower end of the polycrystalline material 109. In addition, the vertical positions of the upper rotary shaft 142 and the lower rotary shaft 132 are adjusted so that the light from the halogen lamp 151 is focused on the upper end of the seed crystal 107 and the lower end of the polycrystalline material 109. The atmosphere 102a of the quartz tube 102 is filled with a total pressure of 1 to 2 atmospheres of a mixed gas of nitrogen and oxygen (changed between 100% nitrogen and 100% oxygen).

  When the operator turns on a power switch (not shown), the control unit 106 controls each unit according to the control program and performs single crystal growth control as follows. When the heating unit 105 is turned on, the halogen lamp 151 heats the upper end portion of the seed crystal 107 and the lower end portion of the polycrystalline material 109, melts the heated portion, and forms dissolved droplets. At this time, only the seed crystal 107 is rotated.

Next, the polycrystalline material 109 and the seed crystal 107 are melted while being rotated in the opposite direction so that the polycrystalline material 109 and the seed crystal 107 are sufficiently adapted. When an appropriate β-Ga ₂ O ₃ single crystal melt 108 ′ is formed, the rotation of the polycrystalline material 109 is stopped, and only the seed crystal 107 is rotated so that the polycrystalline material 109 and the seed crystal 107 are opposite to each other. Pull in the direction to form a dash neck that is thinner than the seed crystal 107

Next, the seed crystal 107 and the polycrystalline material 109 are heated by the halogen lamp 151 while rotating in opposite directions at 20 rpm, and the polycrystalline material 109 is pulled upward by the upper rotating shaft 142 at a rate of 5 mm / h. When the polycrystalline material 109 is heated by the halogen lamp 151, the polycrystalline material 109 is melted to form a melt 108 ′, and when it is cooled, β-Ga having a diameter equal to or smaller than that of the polycrystalline material 109 is obtained. _{A 2} O ₃ single crystal 108 is formed. After forming a single crystal having an appropriate length, the produced β-Ga ₂ O ₃ single crystal 108 is taken out.

Next, a method for manufacturing a substrate formed from the β-Ga ₂ O ₃ single crystal 108 is described. When the β-Ga ₂ O ₃ single crystal 108 is grown in the b-axis <010> orientation, the cleavage of the (100) plane becomes strong, and thus a plane perpendicular to the plane parallel to the (100) plane The substrate is cut by cutting. When the crystal is grown in the a-axis <100> orientation and the c-axis <001> orientation, the cleaving properties of the (100) plane and the (001) plane are weakened. There is no restriction on the cut surface.

Next, the effect of the Ga ₂ O ₃ single crystal by the FZ method according to this embodiment will be described.
(A) Since crystals are grown in a predetermined direction, a large β-Ga ₂ O ₃ single crystal 108 having a diameter of 1 cm or more can be obtained.
(B) This β-Ga ₂ O ₃ single crystal 108 has cracking and twinning tendency by using the a-axis <100> orientation, the b-axis <010> orientation, or the c-axis <001> orientation as the crystal axis. Decreases and high crystallinity is obtained.
(C) Since such a β-Ga ₂ O ₃ single crystal 108 can be generated with high reproducibility, the utility value as a substrate of a semiconductor or the like is also high.

<Formation of II-VI Group Compound ZnSe Thin Film>
A thin film exhibiting p-type conductivity made of ZnSe at 350 ° C. is formed on the (101) plane of a β-Ga ₂ O ₃ single crystal by MOCVD (Metal Organic Chemical Vapor Deposition). ZnSe uses dimethyl zinc and H ₂ Se and is doped with N as a p-type dopant in an NH ₃ atmosphere. In this case, N replaces Se as an acceptor. Here, Zn, Cd, and Hg are used as group II elements, and O, S, Se, Te, and Po are used as group VI elements. Examples of II-VI group compounds include ZnSe and ZnO.

<Method for Forming III-V Group Compound Thin Film>
The III-V group compound thin film is formed by MOCVD. B, Al, Ga, In, and Tl are used as group III elements, and N, P, As, Sb, and Bi are used as group V elements. Examples of the III-V group compound include GaN and GaAs.
FIG. 4 shows an atomic arrangement when a thin film made of GaN is grown on the (101) plane of a β-Ga ₂ O ₃ single crystal substrate. In this case, the (001) plane of GaN grows on the (101) plane of the β-Ga ₂ O ₃ single crystal. O (oxygen) atoms 70, 70,... are arranged on the (101) plane of the β-Ga ₂ O ₃ single crystal. In the figure, the O atom 70 is indicated by a solid circle. The lattice constant of the (101) plane of the β-Ga ₂ O ₃ single crystal is a = b = 0.289 nm and γ = about 116 °. The lattice constant in the (001) plane of GaN is a _G = b _G = 0.319 nm and γ _G = 120 °. In the drawing, N (nitrogen) atoms 80 of GaN are indicated by a broken circle.

When a GaN (001) plane is grown on the (101) plane of a β-Ga ₂ O ₃ based single crystal to form a thin film made of GaN, the lattice constant mismatch is about 10%, Mismatching is about 3%. Accordingly, since the atomic arrangement of the O atoms and the N atoms of GaN in the β-Ga ₂ O ₃ single crystal are substantially the same, the thin film made of GaN can have a uniform planar structure. Therefore, even if a thin film made of GaN is formed on the (101) plane of the β-Ga ₂ O ₃ single crystal without using a buffer layer, lattice mismatch does not occur.

Further, by adding In the adjustment lattice constant _β-Ga 2 _{O 3} single crystal, _β-Ga 2 _{O 3} system single crystal (101) lattice constant in plane of GaN (001) face of the grating The constant can be made closer, and the thin film made of GaN can have a more uniform planar structure.

On the other hand, FIG. 5 shows an atomic arrangement when a GaN thin film is grown on an Al ₂ O ₃ based crystal substrate. O (oxygen) atoms 75, 75,... Are arranged on the (001) plane of the Al ₂ O ₃ based crystal. In the figure, the O atom 75 is indicated by a solid circle. The lattice constant of the (001) plane of the Al ₂ O ₃ based crystal is a _A = b _A = 0.475 nm and γ _A = 120 °. The lattice constant in the (001) plane of GaN is a _G = b _G = 0.319 nm and γ _G = 120 °. In the figure, N atoms are indicated by broken circles. When a GaN (001) plane is grown on the (001) plane of an Al ₂ O ₃ based crystal to form a thin film made of GaN, the mismatch of lattice constant is about 30%. Therefore, when forming a thin film made of GaN on an Al ₂ O ₃ based crystal, if a buffer layer is formed and a thin film is not formed on the buffer layer, lattice mismatch occurs and a uniform planar structure You may not be able to have

<Method for forming thin film>
FIG. 6 is a schematic view showing the MOCVD method, and shows a schematic cross section showing the main part of the MOCVD apparatus. FIG. 7 shows a light-emitting element obtained by the MOCVD method. The MOCVD apparatus 20 includes a reaction vessel 21 connected to an exhaust unit 26 having a vacuum pump and an exhaust device (not shown), a susceptor 22 on which a substrate 27 is placed, a heater 23 that heats the susceptor 22, and a susceptor. A control shaft 24 for rotating and vertically moving 22, a quartz nozzle 25 for supplying source gas obliquely or horizontally toward the substrate 27, a TMG (trimethylgallium) gas generator 31, TMA for generating various source gases (Trimethylaluminum) gas generator 32, TMI (trimethylindium) gas generator 33, and the like. In addition, you may increase / decrease the number of gas generators as needed. NH ₃ is used as a nitrogen source, and H ₂ is used as a carrier gas. When forming a GaN thin film, the TMG and _NH 3, when forming the AlGaN thin film, TMA, it is TMG and NH _3, when forming an InGaN thin film, TMI, the TMG and NH ₃ are used.

In order to form a thin film by the MOCVD apparatus 20, for example, the following is performed. First, the substrate 27 is held by the susceptor 22 with the surface on which the thin film is formed facing up, and is installed in the reaction vessel 21. Then, the temperature was 1020 ° C., TMG was flowed at 54 × 10 ⁻⁶ mol / min, TMA was flowed at 6 × 10 ⁻⁶ mol / min, and monosilane (SiH ₄ ) was flowed at 22 × 10 ⁻¹¹ mol / min for 60 minutes. Then, Si-doped Ga _0.9 Al _0.1 N (n-GaN layer) 1a was grown to a thickness of 3 μm.

Further, the temperature was 1030 ° C., TMG was 54 × 10 ⁻⁶ mol / min, bisdiclopentadienylmagnesium (Cp ₂ Mg) was flown, and Mg-doped GaN (p-GaN layer) 1b was formed to a thickness of 1 μm. Grown up. A transparent electrode (Au / Ni) 1h was deposited thereon, and then Mg-doped GaN 1b was made p-type. Thereafter, the p electrode 1c is attached to the transparent electrode 1h, and the lead 1f is attached by bonding 1e. An n-electrode 1 d was attached to the lower surface of the substrate 1 to constitute a light emitting element.

  The electrode is formed by vapor deposition, sputtering, or the like on a thin film or substrate that exhibits p-type conductivity, or a thin film or substrate that exhibits n-type conductivity. The electrode is formed of a material that can provide ohmic contact. For example, the thin film or the substrate exhibiting n-type conductivity includes Au, Al, Co, Ge, Ti, Sn, In, Ni, Pt, W, Mo, Cr, Cu, Pb, etc. Two types of alloys (for example, Au—Ge alloy), those forming these in a two-layer structure (for example, Al / Ti, Au / Ni, Au / Co), or ITO can be used. The thin film or substrate exhibiting p-type conductivity includes a simple metal such as Au, Al, Be, Ni, Pt, In, Sn, Cr, Ti, Zn, and at least two alloys (for example, Au-Zn). Alloys, Au-Be alloys), those forming these in a two-layer structure (for example, Ni / Au), ITO or the like.

<Formation of thin films with different carrier concentrations>
For example, an n-GaN layer made of GaN having a carrier concentration lower than that of the n-GaN layer is formed on the n-GaN layer made of GaN, and p-GaN made of GaN is formed on the n-GaN layer having a lower carrier concentration. A p-GaN layer made of GaN having a higher carrier concentration than the p-GaN layer and the p-GaN layer are sequentially stacked. For example, the carrier concentration can be changed by a method such as changing the amount of n-type dopant or p-type dopant.
By using a β-Ga ₂ O ₃ single crystal as a substrate and forming a plurality of n layers and a plurality of p layers having different carrier concentrations, the following effects can be obtained.
(A) By forming the carrier concentration of the n-GaN layer lower than the carrier concentration of the substrate, the crystallinity of the p-GaN layer formed thereon is improved and the light emission efficiency is improved.
(B) By joining the n-GaN layer and the p-GaN layer, a PN junction light-emitting element can be formed. Therefore, light emission with a short wavelength can be achieved by the band gap of GaN.
(C) Since a β-Ga ₂ O ₃ single crystal is used for the substrate, a substrate having high crystallinity and n-type conductivity can be formed.
(D) Since the β-Ga ₂ O ₃ single crystal used for the substrate transmits light in the ultraviolet region, emitted light from ultraviolet light to visible light can be extracted from the substrate side.

<Method for forming buffer layer>
FIG. 8 shows the light emitting element shown in FIG. 7 provided with a buffer layer. An Al _x Ga _1-x N buffer layer (where 0 ≦ x ≦ 1) 1 g is provided between the β-Ga ₂ O ₃ substrate 1 obtained in the present invention and the n-GaN layer 1a. This buffer layer was formed by the above MOCVD apparatus. A pn junction structure is formed on the buffer layer according to the above-described <Film formation method>.

Examples of the present invention will be described below.
<Example 1-Method of forming an n-type GaN thin film on a substrate exhibiting p-type conductivity>
A substrate exhibiting p-type conductivity is manufactured as follows. First, β-Ga ₂ O ₃ crystal is formed by FZ method. As a raw material, for example, β-Ga ₂ O ₃ containing MgO (p-type dopant source) is uniformly mixed, and the mixture is put into a rubber tube and cold-compressed at 500 MPa to form a rod shape. The molded product is sintered at 1500 ° C. for 10 hours in the air to obtain a β-Ga ₂ O ₃ -based polycrystalline material containing Mg. Prepare the _β-Ga 2 _{O 3} seed crystal, under a growth atmosphere total pressure 1-2 atm under a flow of _{N 2} and _{O 2} mixed gas at _{500ml / min, β-Ga 2} O 3 or in a quartz tube The crystal is brought into contact with the β-Ga ₂ O ₃ -based polycrystalline material, the part is heated, and both are melted at the contact portion between the β-Ga ₂ O ₃ seed crystal and the β-Ga ₂ O ₃ -based polycrystalline material. To do. When the dissolved β-Ga ₂ O ₃ -based polycrystalline material is grown together with the β-Ga ₂ O ₃ seed crystal in the opposite direction at a rotation speed of 20 rpm and at a growth rate of 5 mm / h, β-Ga ₂ O _A transparent β-Ga ₂ O ₃ single crystal containing Mg is formed on the _three seed crystals. When a substrate is produced from the β-Ga ₂ O ₃ single crystal and the substrate is annealed in an oxygen atmosphere at a predetermined temperature (for example, 950 ° C.) for a predetermined period, oxygen defects are reduced and p-type conductivity is exhibited. A substrate is obtained.

A thin film exhibiting n-type conductivity is formed on the substrate. The thin film is formed by vapor phase growth by MOCVD. First, a substrate showing p-type conductivity is set in an MOCVD apparatus. Holding the substrate temperature to 1150 ° C., the _{H 2} 20l / min, the NH ₃ 10l / min, monosilane (SiH diluted 1.7 × ^{10 -4} mol / min TMG, and with _{H 2} up to 0.86ppm ₄ ) is supplied at a rate of 200 ml / min for 30 minutes to form a thin film made of GaN having n-type conductivity with a film thickness of about 2.2 μm and a carrier concentration of 1.5 × 10 ¹⁸ / cm ³ .

Example 2 Method for Forming Light-Emitting Element with Pn Junction
FIG. 9 shows a light emitting device according to Example 2 of the present invention. The light emitting element 40 includes a Ga ₂ O ₃ substrate 41 made of a β-Ga ₂ O ₃ single crystal and a buffer layer made of Al _x Ga _1-x N formed on the Ga ₂ O ₃ substrate 41 (however, 0 ≦ x ≦ 1) 42, an n-GaN layer 43 made of GaN formed on the Al _x Ga _1-x N buffer layer 42, and a p-type made of GaN formed on the n-GaN layer 43. GaN layer 44, transparent electrode 45 formed on p-GaN layer 44, bonding electrode 47 made of Au or the like formed on a part of transparent electrode 45, and formed on the lower surface of Ga ₂ O ₃ substrate 41. N electrode 46 formed. The light emitting element 40 is mounted on the printed circuit board 50 through a metal paste 51 by attaching leads 49 by bonding 48 through bonding electrodes 47.

The light emitting element 40 emits light at a pn junction where the n-GaN layer 43 and the p-GaN layer 44 are joined, but the emitted light is transmitted as an outgoing light 60 that passes through the transparent electrode 45 and is emitted upward. In addition, the emitted light 61 directed toward the lower surface of the Ga ₂ O ₃ substrate 41 is reflected by the metal paste 51 and emitted upward, for example. Accordingly, the emission intensity is increased as compared with the case where the emitted light is directly emitted to the outside.

Example 3 Flip Chip Type Light Emitting Element
FIG. 10 shows a light-emitting device according to Example 3 of the present invention. The light emitting element 40 includes a Ga ₂ O ₃ substrate 41 made of β-Ga ₂ O ₃ single crystal and a buffer layer made of Al _x Ga _1-x N below the Ga ₂ O ₃ substrate 41 (where 0 ≦ x ≦ 1) 42, an n-GaN layer 43 made of GaN below the Al _x Ga _1-x N buffer layer 42, and a p-GaN layer 44 made of GaN formed on a part of the lower portion of the n-GaN layer 43. And an n-electrode 46 and a p-electrode 52 below the p-GaN layer 44. The p electrode 52 and the n electrode 46 are connected to lead frames 65 and 66 through solder balls 63 and 64, respectively.
The light emitting element 40 emits light at a pn junction where the n-GaN layer 43 and the p-GaN layer 44 are joined. The emitted light passes through the Ga ₂ O ₃ substrate 41 and is emitted upward as outgoing light 60. To exit.

Example 4 Light-Emitting Element with Double Heterostructure
FIG. 11 shows a light-emitting device according to Example 4 of the present invention. The light-emitting element 40 includes a Ga ₂ O ₃ substrate 41 made of a β-Ga ₂ O ₃ single crystal and a buffer layer made of Al _y Ga _1-y N formed on the Ga ₂ O ₃ substrate 41 (however, 0 a ≦ y ≦ 1) 42, and _n-Al z _{Ga 1-z} n cladding layer (where 0 ≦ z <1) 55 made of formed _Al z _{Ga 1-z} n on the buffer layer 42, n- An In _m Ga _1-m N light emitting layer (where 0 ≦ m <1) 56 made of In _m Ga _1-m N formed on the Al _z Ga _1-z N cladding layer 55, and In _m Ga _{1- A} p-Al _p Ga _1-p N clad layer (provided that 0 ≦ p <1, p> z) 57 made of Al _p Ga _1-p N and formed on the _m N light emitting layer 56, and p-Al _p Ga _1-p and the transparent electrode 45 formed on the N-cladding layer 57, the transparent electrode 45 A bonding electrode 47 made of Au or the like formed on the parts, consisting of _Ga 2 _{O 3} n electrode 46 formed on the lower surface of the substrate 41. The light emitting element 40 is mounted on a printed circuit board 50 via a metal paste 51 by attaching leads 49 to bonding electrodes 47 by bonding 48.

The band gap energy of the n-Al _z Ga _1-z N cladding layer 55 is larger than the band gap energy of the In _m Ga _1-m N light emitting layer 56, and the band gap of the p-Al _p Ga _1-p N cladding layer 57. The energy is formed so as to be larger than the band gap energy of the In _m Ga _1-m N light emitting layer 56.

Since the light-emitting element 40 has a double hetero structure, the probability that electrons and holes serving as carriers are confined in the In _m Ga _1-m N light _- emitting layer 56 and recombined increases. The light rate is greatly improved. Further, the emitted light is emitted to the outside as emitted light 60 that passes through the transparent electrode 45 and is emitted upward, and emitted light 61 directed toward the lower surface of the Ga ₂ O ₃ substrate 41 is, for example, by a metal paste 51. Since the light is reflected and emitted upward, the emitted light intensity is increased as compared with the case where the emitted light is directly emitted to the outside.

It is a graph showing the temperature change of the specific resistance of _β-Ga 2 _{O 3.} It is a partially broken perspective view which shows the crucible inserted in the EFG method pulling furnace used by this invention. It is principal part sectional drawing which shows the FZ method infrared heating single crystal manufacturing apparatus used by this invention. Is a diagram showing the atomic arrangement when grown thin films of GaN of (001) plane preferably β-Ga ₂ O ₃ system single crystal substrate (101) of the used on the surface in the present invention. It is a diagram showing the atomic arrangement when grown thin films of GaN of (001) plane in the _Al 2 _{O 3} system of the substrate crystal (001) plane as a comparative example. It is the schematic which shows the MOCVD method used by this invention. It is sectional drawing which shows the light emitting element which concerns on Example 1 of this invention. It is sectional drawing of the light emitting element which provided the buffer layer in the light emitting element which concerns on Example 1 of this invention. It is sectional drawing which shows the light emitting element which concerns on Example 2 of this invention. It is sectional drawing which shows the light emitting element which concerns on Example 3 of this invention. It is sectional drawing which shows the light emitting element which concerns on Example 4 of this invention.

Explanation of symbols

1 substrate 1a n-GaN layer 1b p-GaN layer 1c p electrode 1d n electrode 1e bonding 1f lead 6 crucible 7 seed crystal 8 slit die 8a slit 9 Ga ₂ O ₃ melt 10 β-Ga ₂ O ₃ growth crystal 20 MOCVD Device 21 Reaction vessel 22 Susceptor 23 Heater 24 Control shaft 25 Quartz nozzle 26 Exhaust part 27 Substrate 31, 32, 33 Gas generator 40 Light emitting element 41 Substrate 42 Al _x Ga _1-x N buffer layer 43 n-GaN layer 44 p- GaN layer 45 transparent electrode 46 n-electrode 47 bonding electrode 48 bonding 49 leads 50 printed circuit board 51 metal paste 52 p electrode _{55 n-Al z Ga 1-} z n cladding layer 56 _{In m Ga 1-m} n light-emitting layer 57 p- al _p Ga _1-p N cladding layer 60 emits light 61 emitting light 63, 64 solder baud 65, 66 Lead frame 100 Infrared heating single crystal manufacturing apparatus 102 Quartz tube 102a Atmosphere 103 Seed rotating unit 104 Material rotating unit 105 Heating unit 106 Control unit 107 Seed crystal 108 Single crystal 108 'Dissolved material 109 Polycrystalline material 109a Upper end 131 Lower Drive unit 132 Lower rotary shaft 133 Seed chuck 141 Upper drive unit 142 Upper rotary shaft 143 Material chuck 151 Halogen lamp 152 Elliptical mirror 153 Power supply unit

Claims (3)

A Ga ₂ O ₃ single crystal substrate and a pn junction formed on the substrate, the substrate including an additive for adjusting a lattice constant or a band gap, and the pn junction on the substrate A GaN-based compound semiconductor thin film of one conductivity type formed, and a GaN-based compound semiconductor thin film of another conductivity type opposite to the one-conductivity type formed on the GaN-based compound semiconductor thin film of the one conductivity type. A light-emitting element.   2. The light emitting device according to claim 1, wherein the additive is at least one selected from the group consisting of Cu, Ag, Zn, Cd, Al, In, Si, Ge, and Sn. The substrate is represented by (Al _x In _y Ga _(1-xy) ) ₂ O ₃ (where 0 ≦ x <1, 0 ≦ y <1, 0 ≦ x + y <1). The light emitting device according to claim 1.